This invention relates to a machine for the homogenization and thermal treatment of liquid and semi-liquid food products such as, for example ice creams, whipped cream, creams, chocolate, yogurt and the like.
It should be noted that machines for the homogenization and thermal treatment of liquid and semi-liquid food products such as, for example ice creams, whipped cream, creams, chocolate, yogurt and the like are machines which perform operations such as heating (intended, for example, to facilitate mixing of the ingredients of the mixture), pasteurization (in the typical sense of thermal treatment), homogenization (that is to say, preventing and/or delaying the natural tendency of the substances in the mixture to separate), aging (that is to say, allowing the product to rest at a suitable temperature) and storage (that is, keeping the product at a low temperature until used).
Known in the prior art are many machines for the homogenization and thermal treatment of liquid and semi-liquid food products such as ice creams, whipped cream, creams, chocolate, yogurt and the like, comprising a containment tank having on the bottom of it a vessel pump for circulating the mixture and equipped with an electrical heater and a cooling circuit.
In machines of this kind, the vessel pump causes the mixture to circulate inside the tank and at the same time also heats and then cools the mixture itself.
More specifically, when the pump blade comes into operation, the mixture in the tank is drawn into the pump vessel and then returned to the tank, thereby stirring and blending the mixture.
When the electrical heater is activated, the mixture circulating through the pump is subjected to heating characterized by high heat exchange coefficients. Generally speaking, when the mixture reaches the desired temperature (whether for low, medium or high pasteurization), the heater is switched off and the cooling circuit switched on until the mixture reaches a steady state at the aging or storage temperature (a low temperature around 2° to 6° C.).
The electric heater usually consists of an electrical heating element mounted in the wall of the pump and/or of the tank and heated by the Joule effect.
The cooling circuit, on the other hand, consists of the evaporator of a cooling system coiled around the pump liner and/or the side wall of the tank.
The prior art machines described briefly above have several disadvantages.
Mounting the electric heater on the bottom of the vessel pump or on the side wall of the tank does not guarantee optimum transmission of heat to the mixture circulating in the pump. Heating the mixture may therefore take a very long time since the operating temperature of the heating element cannot be raised too much (without the risk of locally overheating the mixture).
It is also extremely difficult to control the local temperature of the heating elements and to prevent the formation of hot spots (leading to local overheating and burning of the mixture).
Further, it has proved extremely complex to mount the electric heating element in the same way as the evaporator of the cooling circuit because the surface available for heat exchange is not large enough for both.
Further, since a complete thermal treatment cycle comprises heating, holding the temperature, cooling and again holding the temperature, it is necessary to strike a compromise which optimizes both steps of heating and cooling.
Moreover, again in connection with this aspect, in the transient from heating and/or holding the temperature to cooling, the process is significantly slowed by the thermal inertia of the heating elements and of the mass of mixture, delaying the treatment of the food mixture.
Lastly, the above machines consume large amounts of electricity, thus increasing machine running costs considerably.